A collection of useful sailing, sail trimming and news items from OneSails GBR

Wednesday, 4 December 2013

Rating optimisation for IRC - some basic tips

Over
the course of any season, in yacht club bars the length and breadth of the
country boat owners and crew can be found exhaustively discussing ways to
improve the rating of a given boat, particularly at this time of year when the season is over for most people and everyone's had a chance to reflect on what might have been.For
most people optimising the rating means driving the rating down and for some this can be
something of an all encompassing ongoing quest. However, reducing the rating
isn’t necessarily the best thing to do. Let’s just consider what we mean by
optimisation:

"Optimisation" is the
act of balancing a set of variables such that the detrimental effects of each
variable are minimized while maximizing the beneficial aspects of each
variable.

In other words, optimising the rating could mean that the rating goes up in
order to strike the right balance between the salient variables. If the rating
goes up by 2% but the boat goes 3% faster then clearly that is a good thing! This
article is not concerned with the kind of intricate and complex optimisation
that might be found on a TP52 programme, rather the kinds of things that the
everyday club/regatta boat might consider. Following are a couple of examples
of the kinds of typical conversations that we have with owners on a regular
basis.

Firstly, there is the owner of a boat with overlapping headsails who wants
to reduce their rating by re-rating their boat with just their No.3 jib. It’s
pretty easy in principle, reducing the sail area will reduce the rating. But
the boat will go slower, don’t ever forget that! There are several potential
problems with this sort of argument. Most ‘modern’ boats are designed with
non-overlapping headsails from the outset and they will typically have 2 or 3
‘Coded’ Jibs that are all virtually the same size but which are designed to
have different flying shapes to accommodate different wind ranges from zero
wind upwards. The owner that wants to ‘re-rate with a No.3’ is forgetting that
this is a sail that he would usually use in stronger winds and it is therefore
not suited to be used further down the wind range because it is too heavy and too
flat. So, rating the boat with the token No.3 will require the purchase of at
least one more sail that is designed specifically to accommodate lower wind
speeds.

This approach also ignores the fact that the boat was originally designed
with large headsails for a reason; it needs the horsepower! Reducing sail area
is likely to leave the boat horribly short of power in lighter winds and it
will therefore struggle to be competitive. There are mitigating circumstances
of course. If you tend to sail in an area where the breeze rarely drops below
say 12 knots then you would argue that this is sensible optimisation as you
might not spend much time sailing around with the overlapping genoas anyway so
there’s no point in sailing around with the extra rating. These points are
generalisations of course; some boats will be more suited to the idea than
others. With sufficient budget and technical capability you could work out what
was likely to work and what wasn’t. However that is outside of the remit of
most people so your best clues will likely come from looking at what similar
boats have done and how successful they are as a consequence.

The second popular talking point concerns spinnaker area. In general, IRC
seems to encourage higher areas than what would have been considered the norm a
few years ago, particularly in small to medium sized boats where light
displacement is discouraged. Increasing downwind sail area seems to provide a
good trade off between rating and performance. In other words, spinnaker area seems
to be relatively cheap in terms of rating. However, care must be taken;
carrying more spinnaker area is going to be beneficial in lighter airs but if
the boat becomes unmanageable in even moderate conditions (something that we
see only too often) then the boat ends up sailing a disproportionate amount of
time rated for a spinnaker area that it cant use.

From just looking at these two examples it is pretty clear that there are
many things to think about and some of them may not be that obvious from the
outset. In optimising the rating it is important therefore to consider a number
of different things:

·The type of sailing you are planning on doing

·The likely conditions that you are likely to encounter

·The boats that you are likely to be sailing against

·It is generally advantageous to be one of the highest
rated boats in a given class so there may be a case of artificially reducing
the rating via sail area (within limits) in order to sail in the next class
down

·Likewise you might want to increase your rating via sail
area in order to get you towards the top end of the rating band if that means
that you are sailing in clean air more readily.

·Consider manageability; for example, if you find yourself
regularly short tacking against the tide then the ease of tacking a smaller
non-overlapping headsail might outweigh the decrements associated with having a
slower boat.

·The characteristics of the boat itself; extra sail area
won’t increase a displacement boats ‘hull speed’ but it will however help the
boat to achieve its hull speed more readily and improve its average speed. It
won’t however turn a displacement boat into a planing boat.

·In addition make sure that your sails are re-measured
regularly. Laminate sails shrink as they age and this is often enough to save a
point or two.

Please feel free to give us a call to discuss what might work for you…..